The early history of the controversy must be pieced together from about 35 documents found in various sources. The Trinitarian historian Socrates of Constantinople reports that Arius first became controversial under the bishop Athanasius of Alexandria, when Arius made the following syllogism: he said, "If the Father begat the Son, he that was begotten had a beginning of existence: and from this it is evident, that there was a time when the Son was not. It therefore necessarily follows, that he had his substance from nothing".

Bishop Alexander of Alexandria was criticised for his slow reaction against Arius. Like his predecessor Dionysius, he has been charged with vacillation. The question that Arius raised had been left unsettled two generations previously. Therefore Alexander allowed the controversy to continue until he felt that it had become dangerous to the peace of the Church. Then he called a council of bishops and sought their advice. Once they decided against Arius, Alexander delayed no longer. He deposed Arius from his office, and excommunicated both him and his supporters.

But "Arianism" could no longer be contained within the Alexandrian diocese. By the time Bishop Alexander finally acted against his recalcitrant presbyter, Arius's doctrine had spread far beyond his own see; it had become a topic of discussion—and disturbance—for the entire Church. The Church was now a powerful force in the Roman world, with Constantine I having legalized it in 313 through the Edict of Milan. The emperor had taken a personal interest in several ecumenical issues, including the Donatist controversy in 316, and he wanted to bring an end to the Arian dispute. To this end, the emperor sent Hosius, bishop of Córdoba to investigate and, if possible, resolve the controversy. Hosius was armed with an open letter from the Emperor: "Wherefore let each one of you, showing consideration for the other, listen to the impartial exhortation of your fellow-servant." But as the debate continued to rage despite Hosius' efforts, Constantine in AD 325 took an unprecedented step: he called a council to be composed of church prelates from all parts of the empire to resolve this issue, possibly at Hosius' recommendation.[1]

All secular dioceses of the empire sent one or more representatives to the council, save for Roman Britain; the majority of the bishops came from the East. Pope Sylvester I, himself too aged to attend, sent two priests as his delegates. Arius himself attended the council, but his bishop, Alexander, did not, but instead, he sent his young deacon, Athanasius in place of him. Athanasius would become the champion of the Trinitarian dogma ultimately adopted by the council and spend most of his life battling Arianism. Also there were Eusebius of Caesarea and Eusebius of Nicomedia. Before the main conclave convened, Hosius initially met with Alexander and his supporters at Nicomedia.[2] The council would be presided over by the emperor himself, who participated in and even led some of its discussions.[1]

At this First Council of Nicaea twenty-two bishops, led by Eusebius of Nicomedia, came as supporters of Arius. But when some of Arius's writings were read aloud, they are reported to have been denounced as blasphemous by most participants.[1] Those who upheld the notion that Christ was co-eternal and con-substantial with the Father were led by the young archdeacon Athanasius. Those who instead insisted that God the Son came after God the Father in time and substance, were led by Arius the presbyter. For about two months, the two sides argued and debated,[3] with each appealing to Scripture to justify their respective positions. Arius maintained that the Son of God was a Creature, made from nothing; and that he was God's First Production, before all ages. And he argued that everything else was created through the Son. Thus, said Arius, only the Son was directly created and begotten of God; furthermore, there was a time that He had no existence. He was capable of His own free will, said Arius, and thus "were He in the truest sense a son, He must have come after the Father, therefore the time obviously was when He was not, and hence He was a finite being."[4] Arius appealed to Scripture, quoting verses such as John 14:28: "the Father is greater than I". And also Colossians 1:15: "the firstborn of all creation." Thus, Arius insisted that the Father's Divinity was greater than the Son's, and that the Son was under God the Father, and not co-equal or co-eternal with Him.

According to some accounts[who?] in the hagiography of Nicholas of Myra, debate at the council became so heated that at one point, he slapped Arius in the face. Under Constantine's influence, the majority of the bishops ultimately agreed upon a creed, known thereafter as the Nicene creed. It included the word homoousios, meaning "consubstantial", or "one in essence", which was incompatible with Arius' beliefs.[5] On June 19, 325, council and emperor issued a circular to the churches in and around Alexandria: Arius and two of his unyielding partisans (Theonas and Secundus)[5] were deposed and exiled to Illyricum, while three other supporters—Theognis of Nicaea, Eusebius of Nicomedia and Maris of Chalcedon—affixed their signatures solely out of deference to the emperor. However, Constantine soon found reason to suspect the sincerity of these three, for he later included them in the sentence pronounced on Arius.[citation needed]

In 359, the western council met at Ariminum. Ursacius of Singidunum and Valens of Mursa declared that the Son was like the father "according to the scriptures," following a new (Homoian) creed drafted at Sirmium (359). Many of the most outspoken supporters of the Creed of Nicaea walked out. The council, including some supporters of the older creed, adopted the newer creed.[6][7] After the council, Pope Liberius condemned the creed of Ariminum, while his rival, Felix, supported it.[8]

An earthquake struck Nicomedia, killing the bishop Cecropius of Nicomedia, and in 359 the eastern council met at Seleucia Isauria instead. The council was bitterly divided, and procedurally irregular, and the two parties met separately and reached opposing decisions. Basil of Ancyra and his party declared that the Son was of similar substance to the Father, following a (Homoiousian) Creed of Antioch from 341, and deposed the opposing party. Acacius of Caesarea declared that the Son was like the Father, introducing a new (Homoian) creed.[8][9] The Son was begotten - generated from God's own substance.

Constantius requested a third council, at Constantinople (359), of both the eastern and western bishops, to resolve the split at Seleucia. Acacius now declared that the Son was like the Father "according to the scriptures." Basil of Ancyra, Eustathius of Sebaste, and their party again declared that the Son was of similar substance to the Father, as in the majority decision at Seleucia. Maris of Chalcedon, Eudoxius of Antioch, and the deacons Aëtius and Eunomius declared that the Son was of a dissimilar substance from the Father.[10][11] The Heteroousians defeated the Homoiousians in an initial debate, but Constantius banished Aëtius,[10] after which the council, including Maris and Eudoxius,[11] agreed to the homoian creed of Ariminum with minor modifications.[10][11]

The Greek word Logos (λόγος) is traditionally translated as “Word.” French translations of the Bible or other Christian texts often use “Verbe” which word may be read as both 'word', 'utterance' and 'verb', and so has a dynamic quality. The English “Message” or “Expression of the Mind” may also be appropriate attempts to convey the nuance of the Greek concept. The Jewish-Alexandrian theologian and philosopher Philo wrote extensively about the Logos in ways that are reminiscent of New Testament theology.[citation needed] For instance, his teaching that “For the Logos of the living God being the bond of every thing, as has been said before, holds all things together, and binds all the parts, and prevents them from being loosened or separated” echoes Colossians 1:17.[citation needed]

Dominating the secular intellectual milieu in which the Cappadocians lived was Platonism, which, when mixed with Christian theology, bred Arianism, the most prominent heresy at the dawn of the 4th century. According to Platonism, the One or “first cause” radiated immaterial and material entities in a hierarchical, categorized way. If this conceptualization had remained unchecked, the Christian God could have been given a Platonic veneer: the Father as the “first cause,” the Son or Logos as the primary emanation from the One, and the Spirit as a further emanation of the Logos. Arianism held that the Son of God was a being created by the First Person and could not be considered divine, an attractive option incorporating both classical Greek thought and the historical event of the person of Jesus. The Cappadocians vehemently argued against Arianism for its inequality among the divine Persons: “This was the disease of Arius, who gave his name to the madness, and who threw into confusion and brought to ruin a great part of the Church. Without honoring the Father, he dishonored what proceeded from Him by maintaining unequal degrees in the Godhead. But we recognize one glory of the Father, the equality of the Only-begotten, and one glory of the Son, the equality of the Holy Spirit. And we believe that to subordinate anything of the Three is to destroy the whole” (Gregory of Nazianzus, On St. Basil, par. 30.). The Cappadocian insistence on equality among the divine Persons was also a solid refutation of the hierarchical ordering of the cosmos found in Platonism.

According to a belief related to Arianism, Anomoianism, the Spirit was subjugated to the Father and the Son. As time went on, arguing for the divinity of the Spirit became increasingly more important to the Cappadocians. Nicaea left rather open the question of the divinity of the Spirit; belief “in the Holy Spirit” was all the bishops had stated. Advocating for the divinity of the Holy Spirit was crucial for the Cappadocians exactly because of their insistence on the unity and equality of the Three: “The central thrust of Basil’s positive argument in favor of the Spirit’s deity is the non-separability of the three persons and the inference from this that they are all three worthy of this same honor” Anthony Meredith, The Cappadocians (Crestwood, New York: St. Vladimir’s Seminary Press, 1995), 32).

The Cappadocians’ insistence on three co-equal divine Persons, however, subjected them to accusations of tritheism. The extreme opposite, Sabellianism, also widespread at that time, conflated the three Persons into one and saw no distinctions among them whatsoever. The theologians, therefore, had to articulate the unity of the divine essence as well as the distinctness of Persons in the Godhead.

As time went on and in response to continual controversy, the Cappadocians’ theological writings increased in nuance and also in clarity. What emerged from them was the orthodox Christian belief that God is a unity of Three distinct yet inseparable and equal Persons. The Cappadocian theologians worked out this theology by establishing the distinctness of the divine Persons, the communitarian relationships of the Three, and the unity of their divine essence.

In Christianity, Easter is the Sunday after Passover. However, it was debated whether to follow Jewish practice for the calculation of the date of Passover. By the 4th century, the most common Christian methods had diverged from the most common Jewish ones.[16]

Many held that presbyters and bishops should not marry, and some held that presbyters and bishops who had already married, and their wives, should refrain from sex.[17]

Eustathius of Sebaste condemned marriage entirely; he also excluded married presbyters from communion, forbade married Christians from praying at home while encouraging unmarried ones to hold services at home; he was deposed for this and his doctrines were condemned.[18]

The Homoousians taught that the Son is of the same substance as the Father, i.e. both uncreated. The Sabellian form had been condemned as heresy in the 3rd century. The Athanasian form would be declared orthodox at the Council of Constantinople in 383, and has become the basis of most of modern trinitarianism.[19]

This article is missing information about Eusebius' criticisms of Marcellus' theology, Athanasius' defense of Marcellus, and modern scholarly research on these figures. Please expand the article to include this information. Further details may exist on the talk page.(March 2008)

The Homoians taught that the Son is similar to the Father, either "in all things" or "according to the scriptures," without speaking of substance.[42] Several members of the other schools, such as Hosius of Cordoba and Aëtius, also accepted certain Homoian formulae.[57]

Ursacius, initially homoiousian, then homoousian, and later homoian bishop of Singidunum, who had opposed Athanasius.[58]

Valens, initially homoiousian, then homoousian, and later homoian bishop of Mursa, who had opposed Athanasius.[58]

^Bernhard Lohse, A Short History of Christian Doctrine, pp. 56-59 & 63.
Peter Heather & John Matthews, Goths in the Fourth Century, pp. 127-128. This mainly discusses the later controversy and only mentions Athanasius' form.

^Socrates of Constantinople, Church History, book 1, chapter 36 and book 2, chapter 20
Socrates, book 1, chapter 36, states that Marcellus "dared to say, as the Samosatene had done, that Christ was a mere man" and book 2, chapter 18, states that Photinus "asserted that the Son of God was a mere man."

^Socrates of Constantinople, Church History, book 1, chapter 36 and book 2, chapter 29.
Sozomen, Church History, book 4, chapter 6.
Besides these histories, Eunomius' First Apology associates Marcellus' and Photinus' doctrines with Sabellius, and condemns these doctrines.'

^Socrates of Constantinople, Church History, book 1, chapter 36 and book 2, chapter 20.

^Philostorgius, in Photius, Epitome of the Ecclesiastical History of Philostorgius, book 3, chapter 5, book 4, chapter 12 and book 6, chapter 5 refer to "different substance," book 4, chapter 12 refers to "dissimilarity of substance," and book 4, chapters 4 & 12 and book 5, chapter 1 refer to "unlike in substance" or "unlikeness in substance."

^Peter Heather & John Matthews, Goths in the Fourth Century, pp. 127-128. This mainly discusses the later controversy and only mentions Anomoeanism, without using the term Heteroousian.